1. Field of the Invention
The present invention relates to a magnetic material detecting device, and more particularly to a magnetic material detecting device of which magnetic material detection accuracy is improved by disposing a magnetic material detecting coil to enable to detect the magnetic material in a large area.
2. Description of the Related Art
In recent years, there are provided various methods and devices to enhance security such as prevention of leakage of confidential information, personal information and the like, prevention of counterfeiting of valuable securities and the like, and theft-prevention of commodities and the like. For example, there is known a copy-protected printed material for prevention of counterfeiting.
The above copy-protected printed material is configured to prevent it from being copied illegally for counterfeiting by forming latent images having different reflectivity and hue on printing paper to make it hard to copy by the difference in reflectivity and hue of the latent images formed on the printing paper or to copy in such a way enabling to discriminate as a reproduction when the printed material which is printed on the printing paper is copied by a monochrome copy machine or a color copy machine.
But, such a method needs to scan the print sheet or to emit light from a prescribed direction in order to detect the latent images having different reflectivity and hue formed on the print sheet, and it is desired to propose methods and devices for disabling unauthorized copying without performing the above operation.
There is also known a device security management system that is configured to make a user carry an RFID (Radio Frequency Identification) and also to attach an RFID to confidential documents and to prohibit copying according to information read from the RFIDs so that unauthorized copying of a printed material having confidential information or the like printed on it can be prohibited.
The above-described device security management system requires the user to always carry the RFID. Therefore, it is desired that a method and a device capable of surely preventing a printed material from being copied without authorization without placing a heavy burden on the user.
Lately, in libraries, supermarkets, various types of rental shops and the like, an antitheft system, that a medium to be detected which can be detected without contacting is applied to mediums such as books, commodities and the like and a detecting device for detecting the medium to be detected is disposed near the exit in order to prevent the books, commodities and the like from being stolen, is becoming widely popular.
The above antitheft system is configured such that if a medium is attempted to be wrongfully taken out, the detecting device disposed in the vicinity of the exit detects the medium to be detected, which is attached to the medium, without contacting and activates an alarm or the like to prevent the medium from being stolen.
For example, there is known a magnetic tape detecting device that can detect not only the presence or not of a magnetic tape which is used to prevent books and commodities from being taken wrongfully but also the number of magnetic tapes. Further improvement of the magnetic tape detection accuracy enables to apply the magnetic tape detecting device to various kinds of uses for prevention of a fraudulent procedure, settlement of amount and the like involved in, for example, self-service in a library to borrow a book and an unmanned shop.
In order to further improve the magnetic tape detection accuracy, the above-described magnetic tape detecting device has plural detecting coils linearly connected in the same winding direction and plural bias coils for applying a bias magnetic field to the magnetic tapes connected with mutually adjacent bias coils linearly connected in the opposite winding direction from each other, thereby controlling a direction in that the magnetic tapes are magnetized by external magnetic fields which are emitted from the plural bias coils and detecting the number of magnetic tapes according to the detected result of the pulse magnetic fields emitted by the magnetic tapes.
But, the above-described magnetic tape detecting method needs to limit the positional relationships of the magnetic tapes, the detecting coils and the bias coils to some extent in order to further improve the magnetic tape detection accuracy.
For example, where the above-described magnetic tape detecting device is applied as an antitheft device to detect the magnetic tape given to a medium by the magnetic tape detecting device disposed in the vicinity of the exit, it is general that a magnetic field distribution has a characteristic that it attenuates sharply than an electric field distribution when it comes far from the center of the magnetic field. Therefore, it is hard to control the magnetizing direction of the magnetic tape by the external magnetic fields emitted from the plural bias coils.